Process of reducing the viscosity characteristics of nitrocellulose



Patented une 8, 1926.

. UNITED STATES? PAT NT, OFFICE.

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courm, or aocnnsrsa, new Yonx, a conrona'rron 01' new Yoax.

i '5 PROCESS OF REDUCING TH-t VISCOSITY CHARACTERISTICS OI I TITBOCELLULOSE.

Jlo Drawing.

This invention relates to processes for're ducing the viscosity characteristics of nitrocellulose. One object of the 1 I1V8Il131011 1s to provide a simple and inexpensive'process for 6 reducin' said viscosity characteristics safely and wit in a short time.. .A -further object of" the inventionis to provide a process for reducing'rapidly and" accurately the viscosity characteristics of nitrocellulose when .it is 10 in the solid-colloidized state, and even when mixed with high-boiling organic compounds or softeners. Another object is to provide a process which can be operated at atmosheric pressure and room. temperature.

1' till a further object is to provide a process in which a series of'baths are used in such a way that the material of the first bath can be used re eatedly without contamination by the second bath.. Another object of the 1nvention is to provide a process in which the nitrocellulose is converted into such a state that the acids, which lower the viscosity, can be very easily and quickly washed out of the-nitrocellulose. Still another object of the invention is to provide a process in which the nitrocellulose remains substantially' undissolved, thereby avoiding unnecessary and troublesome. precipitation steps;

Other objects will hereinafter ap ear.

It is highly desirable, when ma ing'solu tions of mtrocellulose for spraying to have a high concentration of nitrocellulose and yet to keep thevisoosity of-the solutions at a low oint. In order to obtain such 'solu-- I have found that a'process of this kind can be carried out by first softening the'nitrocellulosic material with a suitable liquid and thereafter treatin acid solution. The so ning step makes the nitrocellulosic material-more susceptible to the action of the acid and thereby. shortens thetime for producing the desired reduction.

it with an aqueousv Application and semester 1, 1925. semim. 68,951.

Moreover, it makes such reduction more uni- I washing operations.

' Various penetrant liquids may be employed such, for instance, as one that merely 65 softens the nitrocellulosic material, like films, and has a solvent action on the highboiling organic compounds therein, such as camphor, butyl alcohol, triphenyl phos hate, tricresyl phosphate, monochlornapht alone. and the like. It is smoetimes useful to control the action of an especially strong penetrant by diluting it w1th. water, so that it merely softens the nitrocellulose, the action being always stopped before the nitrocellulose itself is dissolved to any substantial extent.

The operations may be carried out' at room temperature and atmospheric pressure. Various acids may be employed in the sec- 0nd step .of the process 1n which the vis-. cosity is reduced. I may for example. em- I ploy a nitric acid bath, especially one con-I taining oxides of nitrogen as indicated in copending application, Serial No. 12,181, C.

U. Prachel, filed Feb. 27, 1925, for process of treating nitrocellulosic materials.

- I shall now describe one embodiment of my invention, but itwill be understood that the latter is not restricted to the details of this'jllustration exce t'as indicated in the appended claims. e nitrocellulosic material is preferably comminuted. Solid colloidized nitrocellulose, such as pyroxylinwaste, or film scrap from which the gelatinous coatings have been removed, is choppedup into small pieces. I

The comminuted material is then treated by the enetrant liquid, say a bath of methyl alco ol toned down by 5% of water. The material is allowed to soften in-contact. with this liquid, say by being immersed in it, for 1 to 5 hours at room temperature and atmospheric pressure. A slight heating is ermissible to, shorten the time of treatment. hus I.may conduct the above 0 erations at 40 C. and stop the action in a out two hours. The action in all forms of'my process is stop ed before any substantial dissolving of t e nitrocellulose takes place, and no before the pieces of nitrocellulosic material gumtogether into an unmanageable mass. This initial leaching step softens the material and leaches out some of the high-boiling organic compounds which are present with the nitrocellulose. It opens up the latter to subsequent treatment to a-surprising degree.

When the pre-leaching step is completed, the nitrocellulosic material is separated from the leaching bath, say by lifting the par- =ticles of the nitrocellulosic material out of the bath and draining them, or running the acid bath may conveniently be a 30% aqueous solution of spent mixed acids from a cellulose nitrating plant. Such a solution may include approximately 20% H SO 10% I-INO and-1 to 2% of nitrogen oxides, say N 0 Of course, there is nothing critical about these proportions, and they may be varied widely without departing from the invention. In fact, other well known acids and acid mixtures may be substituted. I have found the above mixture, however, to be preferable because it acts rapidly and safely at room temperature and has ableaohing tendency which makes other bleaching action practically unnecessary.

The treatment may take place in any suitable acid-resisting container, the pieces of nitrocellulosic material being immersed in the liquid. By conducting the operations at room temperature, the loss of valuable oxides of nitrogen is reduced to a minimum, even when the soaking in the acid lasts for several days. Of course, the vessels may be covered.

The duration of the treatment is con trolled by tests. When samples show that the desired degree of low viscosity has been reached, the acid and nitrocellulose are separated, say by draining off the acid from the material, preferably assisted by pressure on the latter.

Finally the nitrocellulosic material is washed with successive changes of water. The latter may be heated, if desired to hasten the action, say to about 75 C. But by .reason of the opening up of the nitrocellulose by my relatively quickly washed out by successive changes of cold water or water at roomtemperature. The increased thoroughness with which the washing can be carried out, be-

cause of the susceptible condition of the nitrocellulose, results in a very noticeably pro-treatment, the acid can be improved stability of the product when subjected to the usual heat tests.

The concentration of the mixed acids in the second step of the process can be altered considerably. Instead of mixed acids, I may use a single acid, say for instance nitric acid containing some nitrogen oxides. A 6% aqueous solution of nitric acid containing 1.2% of nitrogen oxides has been demonstrated, for example, to operate effectively at room temperature during a treatment of a few days. In general the preferred baths contain from 5 to 2% of HNO 10 to 30% of H SO and A; to 10% of nitrogen oxide.

While I prefer to use in the first step of the process an active nitrocellulosic solvent, toned down by water to the point where it acts merely as a penetrant, I may employ other penetrants which have little, if any, solvent action on the nitrocellulose such as ethyl alcohol.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

1. The process of treating nitrocellulose, which comprises first softening it with a penetrant liquid to make it more susceptible to subsequent treatment, and thereafter acting on it separately with an aqueous acid solution until the viscosity characteristics of the nitrocellulose are reduced.

2. The process of treating solid colloidized nitrocellulose associated with a high-boiling organic compound, which comprises first softening it with a penetrant liquid, which has a solvent action on said organic compounds, and thereafter acting on said material with an aqueous acid solution until the viscosity characteristics of the nitrocellulose are reduced.

3. The process of treating solid colloidized nitrocellulosic material, which comprises softening it with a penetrant liquid containing water and an active nitrocellulose solvent, stopping the action of said liquid before the nitrocellulose is dissolved, and thereafter acting on it with an aqueous acid solution until the viscosity characteristics of the nitrocellulose are reduced.

4. The process of treating solid colloidized nitrocellulose associated with a high-boiling organic compound, which comprises soften-- ing'it with a mixture of water and methyl alcohol to make it more susceptible to subsequentv treatment, stopping the action before the nitrocellulose is dissolved, and thereafter acting on it with an aqueous acid solution until the viscosity characteristics of the nitrocellulose are reduced.

5. The process of treating solid colloidized nitrocellulose, which comprises acting thereon with a penetrant liquid, the action being stopped before the nitrocellulose is dissolved, separating said liquid from the nitrocellulosic material, and thereafter act- 1,5ss,ose

ing on it with an aqueous acid solution until the viscosity characteristics of the nitro cellulose are reduced.

6. The rocess of treating solid colloidized nitrocellu ose, which comprises softening it with a penetrant liquid to facilitate subseuent treatment, separating the bulk of said hquid from said nitrocellulose, and thereafte'r acting on it with an aqueous acid solution containing oxides of nitrogen until the viscosity characteristics of the nitrocellulose are reduced.

7. The process of treating solid colloidized nitrocellulose associated with a high-boiling organic compound, which comprises first treatin it with, a penetrant liquid until its suscept1bility to subsequent liquid treatments is increased, separating said penetrant liquid from said nitrocellulose, acting on said nitrocellulose with an aqueous acid solution until the viscositycharacteristics of the nitrocellulose are reduced, removing the bulk of said acid solution from the nitrocellulose and washing the latter to remove residual acid from it.

8. The rocess of treatin solid colloidized nitrocellu ose associated with a l'iigh-boiling organic compound, which comprises first leaching it with a penetrant liquid which has a solvent action on said organic compound, separating the bulk of said liquid from said nitrocellulose, treating said nitrocellulose with an aqueous acid solution until its viscosity characteristicsare reduced,

and removing and washing out the acid from said nitrocellulose.

Signed at RochestemNew York, this 24th day of August, 1925.

LEONARD E, BEAN CHEN. 

